Shetland Library and Orkney Library, in particular, love nothing more than a bit of back and forth. The most recent example came on Friday, when Shetland Library started bragging on Twitter about their appearance in BBC crime drama Shetland.

J.K. Rowling settles feud between rival libraries in the best way possible

WASHINGTON, : J.K. Rowling, author of the best-selling Harry Potter children's books appears at a book signing 20 October, 1999 in Washington, DC. The books feature Harry Potter as a fictional orphan who attends a school for wizards. The books have become controversial in recent weeks as parents in a South Carolina school district seek to have the books banned for violent content. AFP PHOTO (Photo credit should read TIM SLOAN/AFP/Getty Images)

JK Rowling during Archive Images of JK Rowling at the launch of Harry Potter and The Goblet of Fire at King's Cross Station in London, Great Britain. (Photo by Fred Duval/FilmMagic)

TORONTO, CANADA - OCTOBER 24: Harry Potter author J.K. Rowling waves to the crowd before her reading during the International Festival of Authors at the SkyDome 24 October 2000 in Toronto, Canada. (Photo credit should read AARON HARRIS/AFP/Getty Images)

LONDON - NOVEMBER 4: British author J.K. Rowling, creator of the Harry Potter children's books, and 11 year old Daniel Radcliffe (Harry Potter in the film version) attend the world film premiere of 'Harry Potter and The Philosopher's Stone' at the Odeon Leicester Square cinema in London on November 4, 2001. The movie is titled 'Harry Potter and The Sorcerer's Stone' for it's U.S. release. (Photo by Gareth Davies/Getty Images)

J.K. Rowling (right) during 2002 Child Of Achivement Award at Park Lane Hilton London in London, Great Britain. (Photo by Ferdaus Shamim/WireImage)

LONDON - NOVEMBER 3: The author of the Harry Potter books, J.K. Rowling poses for photographers as she arrives the Harry Potter and the Chamber of Secrets world premiere November 3, 2002 in London. The movie is director Christopher Columbus's second instalment of the series based on J.K. Rowling's tales of wizardry. (Photo by GarethDavies/Getty Images)

EDINBURGH, SCOTLAND - JULY 8: Harry Potter author JK Rowling receives an Honorary Degree of Doctor honoris causa at the University of Edinburgh's graduation ceremony in McEwan Hall on July 8, 2004 in Edinburgh, Scotland. (Photo by Christopher Furlong/Getty Images)

EDINBURGH, UNITED KINGDOM - JULY 15: Harry Potter author JK Rowling arrives at Edinburgh Castle where she will read passages from the sixth magical children?s title ?Harry Potter And The Half-Blood Prince?, on July 15, 2005 in Edinburgh, Scotland. 70 junior reporters from around the world, aged between eight and 16, make up the audience, and get to meet and ask questions of the author ahead of the midnight release of the new volume. (Photo by Christopher Furlong/Getty Images)

UNITED KINGDOM - JULY 16: Author J.K. Rowling poses for photographers at the world launch of her new book 'Harry Potter and the Half-Blood Prince' at Edinburgh Castle in her home city of Edinburgh, Scotland, Saturday morning July 16, 2005. Ms. Rowling read a chapter of the new book to competition winning children. (Photo by Mike Wilkinson/Bloomberg via Getty Images)

Bucharest, ROMANIA: The former special rapporteur on Romania to the European Parliament, Emma Nicholson de Winterbourne (L), Romanian Prime Minister Calin Popescu Tariceanu (C) and British writer J.K. Rowling (R) talk 25 January 2006 during a meeting at the Victoria Palace, the Romanian government headquarters in Bucharest. Rowling, the author of the Harry Potter books, will take part in a charity benefit to help underprivileged children of Romania and Europe. Ten signed copies of her most recent book, 'Harry Potter and the Half-Blood Prince,' will be auctioned off during the event. Of 80,000 abandoned children in Romania, about 50,000 live in foster families and 30,000 in orphanages. AFP PHOTO DANIEL MIHAILESCU (Photo credit should read DANIEL MIHAILESCU/AFP/Getty Images)

Bucharest, ROMANIA: Britain's J.K. Rowling, the author of the internationally best-selling series of books about the young wizard Harry Potter applauds a performance by Romanian orphans during a ceremony in Bucharest, Romania, 26 January 2006. Rowling said 26 January at the start of a two-day visit to Romania that she hoped reforms the country had made in child welfare would benefit other countries in the region. Rowling, 40, recently became a trustee of a new Bucharest-based foundation called The Children's High Level Group, which raises money for children in need and promotes childcare reforms in Romania as a model to other European countries. AFP Photo/Vadim Ghirda/POOL (Photo credit should read VADIM GHIRDA/AFP/Getty Images)

JK Rowling (Photo by Sandy Young/WireImage)

ABERDEEN, UNITED KINGDOM - JULY 06: JK Rowling, the creator of Harry Potter, receives Doctor Of Laws honorary degree from the University of Aberdeen at Marischal College July 6, 2006 in Aberdeen, Scotland. (Photo by Jeff J Mitchell/Getty Images)

LONDON - JUNE 02: (EMBARGOED FOR PUBLICATION IN UK TABLOID NEWSPAPERS UNTIL 48 HOURS AFTER CREATE DATE AND TIME. NO UK MAGAZINES) JK Rowling and Sir Elton John attend the Raisa Gorbachev Foundation Party at Stud House, Hampton Court Palace on June 2, 2007 in Richmond upon Thames, London, England. The night is in aid of the Raisa Gorbachev Foundation - an international fund fighting child cancer. (Photo by Dave M. Benett/Getty Images)

LONDON - JULY 03: Author J.K. Rowling and her guest attend the after party following the European premiere of 'Harry Potter And The Order Of The Phoenix' at the Old Billingsgate Market on July 3, 2007 in London, England. (Photo by Dave Hogan/Getty Images)

LONDON - JULY 21: JK Rowling Launches Seventh and Final Harry Potter Book. 21 July 2007 in the Natural History Museum, London (Photo by Eamonn McCormack/WireImage)

LONDON - OCTOBER 09: JK Rowling attends the Pride of Britain Awards 2007 at Television Centre on October 09, 2007 in London, England. (Photo by Eamonn McCormack/Wireimage)

HOLLYWOOD - OCTOBER 15: Author J.K. Rowling holds a press conference and book signing for Los Angeles Unified School District (LAUSD) school children October 15 2007, at The Kodak Theatre in Hollywood, California. (Photo by Toby Canham/Getty Images)

Author J.K. Rowling (C) arrives at the world premiere of 'Harry Potter and the Half-Blood Prince' in Leicester Square in central London on July 7 2009. The film is the adaptation of the penultimate book in the long-running series about the magical life of the young schoolboy. AFP PHOTO/Leon Neal (Photo credit should read Leon Neal/AFP/Getty Images)

WASHINGTON - APRIL 05: British author J.K. Rowling, creator of the Harry Potter fantasy series, points to the place on her forehead where her title character has a scar while reading 'Harry Potter and the Sorcerer's Stone' during the Easter Egg Roll on the South Lawn of the White House April 5, 2010 in Washington, DC. About 30,000 people are expected to attend attended the 132-year-old tradition of rolling colored eggs down the South Lawn of the White House. (Photo by Chip Somodevilla/Getty Images)

LONDON, ENGLAND - JULY 07: (EMBARGOED FOR PUBLICATION IN UK TABLOID NEWSPAPERS UNTIL 48 HOURS AFTER CREATE DATE AND TIME. MANDATORY CREDIT PHOTO BY DAVE M. BENETT/GETTY IMAGES REQUIRED) Author J.K. Rowling arrives at the World Premiere of 'Harry Potter And The Deathly Hallows Part 2' in Trafalgar Square on July 7, 2011 in London, England. (Photo by Dave M. Benett/Getty Images)

Author JK Rowling (L) stands before being awarded a Benefactors Award by Edinburgh University and the Princess Royal during an open air ceremony on September 26, 2011. The honour is in recognition of a Â£10 million donation made by Rowling to the university last year to establish a new multiple sclerosis (MS) research clinic. AFP PHOTO / PA / David Cheskin (Photo credit should read DAVID CHESKIN/AFP/Getty Images)

LONDON, ENGLAND - NOVEMBER 09: J. K. Rowling attends a charity evening hosted by JK Rowling to raise funds for 'Lumos' a charity helping to reunite children in care with their families in Eastern Europe at Warner Bros Studios on November 9, 2013 in London, England. (Photo by Dave J Hogan/Getty Images)

NEW YORK, NY - APRIL 09: Founder and President of Lumos and Patron of Lumos USA/ Author J.K. Rowling ceremoniously lights the Empire State Building in LumosÃ colors of purple, blue and white to mark the US launch of her non-profit organization at The Empire State Building on April 9, 2015 in New York City. (Photo by Cindy Ord/Getty Images)